Problem: Simplify the following expression: $n = \dfrac{8}{9k} - \dfrac{1}{4k}$
In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $9k$ and $4k$ $\lcm(9k, 4k) = 36k$ $ n = \dfrac{4}{4} \cdot \dfrac{8}{9k} - \dfrac{9}{9} \cdot \dfrac{1}{4k} $ $n = \dfrac{32}{36k} - \dfrac{9}{36k}$ $n = \dfrac{32 -9}{36k}$ $n = \dfrac{23}{36k}$